docs: def get_proxy(self, url):
          """
          Get a proxy to use for a given URL, excluding any banned ones.
  
          :param str url: The URL for which to find an appropriate proxy.
          :return: A proxy to use for the URL,
              or the string 'DIRECT', which means a proxy is not to be used.
              Can be ``None``, which means to not attempt the request.
          :rtype: str|None
          """
          proxies = self.get_proxies(url)
          for proxy in proxies:
              if proxy == 'DIRECT' or proxy not in self._offline_proxies:
                  return proxy